The invention relates to a sensor device for sensing biometric characteristics, in particular finger minutiae, by means of a biometric sensor chip. The sensor chip is fastened on a flexible printed circuit board which comprises a highly flexible substrate layer and conductor tracks that have been applied to the substrate layer, are in electrical contact with the sensor chip, and are led to a terminal region of the flexible printed circuit board.
It has been known heretofore to sense personal characteristics, for example finger minutiae, i.e. fingerprints, by means of biometric fingertip sensors, in order to permit or deny access to an appliance, a room etc. according to the result of the sensing. Such authentication of persons by means of biometric data can be used for example in the case of automated teller machines, mobile phones, and computers.
Prior art sensor devices of this type are usually produced by the sensor chip being mounted on a mounting board, the terminal pads of the sensor chip subsequently being connected to the conductor tracks on the mounting board by means of a wire bonding method and the sensor chip being encapsulated in a composition in order to keep it stable on the mounting board and protect it. Such a configuration is known, for example, from French published patent application FR 2 736 179 A1. There, it is disadvantageous, however, that such a configuration entails a relatively complex production process. Furthermore, the mounting of such a sensor device in the receiving housing is often relatively complicated and tolerance-critical.
Another prior art sensor device is known from European published patent application EP 0 786 745 A2. There, a housing surrounding the sensor chip is formed from a plastic encapsulating composition in such a way that the sensor surface is accessible via an opening in the housing. Furthermore, the international publication WO 98/11500 describes a sensor device in which the sensor is made up of thin metal layers around a flexible plastic substrate.
Conductor tracks on the plastic substrate establish a connection between the sensor and a terminal region of the flexible plastic substrate. However, the construction of the sensor device described in WO 98/11500 is complicated and difficult to fit into different appliances.
The object of the invention is to provide a sensor device for detecting biometric characteristics, such as finger minutiae, which overcomes the above-noted deficiencies and disadvantages of the prior art devices and methods of this kind, and wherein the sensor device can be produced particularly simply and, in addition, can be fitted into appliances in a simple way.
With the above and other objects in view there is provided, in accordance with the invention, a sensor device for sensing biometric characteristics, comprising:
a terminal region;
a flexible circuit board having a highly flexible substrate layer, a plurality of conductor tracks on the substrate layer leading to the terminal region, and a grounding conductor track;
the flexible circuit board having formed therein a through-opening and an electrically conducting grounding frame at least partially surrounding the through-opening on a contact side of the sensor device and being electrically connected with the grounding conductor track of the flexible printed circuit board;
a biometric sensor chip mounted on the flexible printed circuit board and electrically connected to the conductor tracks; and
the sensor chip having a sensor zone, for example for sensing finger minutiae, accessible on the contact side of the sensor device through the through-opening in the flexible printed circuit board.
In accordance with an additional feature of the invention, the conductor tracks are arranged on an underside of the flexible circuit board, and sensor chip pads on an upper side of the sensor chip are electrically connected to the conductor tracks.
In accordance with a concomitant feature of the invention, the highly flexible substrate layer is formed of Kapton(copyright) or of a PET film.
In other words, the sensor chip is fastened on a flexible printed circuit board which comprises a highly flexible substrate material and conductor tracks which have been applied to the substrate material, are in electrical contact with the sensor chip and are led to a terminal region of the flexible printed circuit board.
The sensor device according to the invention offers the advantage that the sensor chips can be mounted and tested on flexible printed circuit boards which are in the form of endless strips or repeats, i.e. relatively large sheets on which there are a plurality of flexible printed circuit boards. The fitting of the sensor devices into the appliances is easy to integrate into the production process and is accordingly inexpensive. The connection between the terminal region of the flexible printed circuit board and the appliance can take place via a standard plug-in connection, for example a zero-insertion-force connector, or a soldered connection. Furthermore, the flexible printed circuit board can be customized, i.e. the length, width, shape of the terminals etc. of the flexible printed circuit board can be designed individually in a simple way. On account of the flexibility of the flexible printed circuit board, the sensor device is also easy to mount when there are relatively great tolerances in the height of the receiving space of the appliance.
The sensor chip is in this case fastened on the flexible printed circuit board in such a way that the sensor zone of the sensor chip is accessible through a through-opening in the flexible printed circuit board. The through-opening in the flexible printed circuit board is surrounded on the contact side at least partially by an electrically conducting grounding frame which is in electrically conducting connection with a conductor track of the flexible printed circuit board. When a finger is placed onto the sensor device, for example, such a grounding frame is inevitably brought into electrical contact by the finger and discharges voltage peaks from the finger to the ground. Such a grounding frame can be applied very simply and in the same way as the conductor tracks to the flexible substrate material of the flexible printed circuit board.
In accordance with an added feature of the invention, a dimensionally stable holding and guiding part is provided and formed with a depression configured to receive therein the sensor chip. The sensor chip is fixed in the depression. Such a holding and guiding part serves for the fastening of the entire sensor device on the appliance, positions the sensor chip by means of the depression and at the same time protects the sensor chip, since the latter is embedded in the depression.
Since the sensor chip is fastened from the underside of the flexible printed circuit board on the latter, it is expedient if the sensor pads, i.e. its terminal contacts, are arranged on the upper side of the sensor chip, so that conductor tracks arranged on the underside of the flexible printed circuit board can be placed directly onto the sensor chip pads and electrically connected to them. This electrical connection may be carried out by known methods such as heat sealing, soldering, thermocompression or thermosonic bonding, wire bonding etc. It is also readily possible, however, to apply the conductor tracks of the flexible printed circuit board additionally or alternatively to the upper side of the substrate layer and bring them into electrical contact through an opening through the substrate layer and the sensor pads.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a sensor device for sensing biometric characteristics, in particular finger minutiae, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.